1. Field of the Invention
This invention relates generally to a head driving apparatus, and more particularly is directed to the fine adjustment device thereof, that is, the device for finely displacing a magnetic head which is driven by such apparatus.
1. Description of the Prior Art
Disclosed in U.S. Pat. No. 4,630,145 is a head driving apparatus, in which a lead screw that is driveably connected to a movable head carriage, is rotatively driven by a coarse stepper motor, and axially displaced by a fine stepper motor so as to finely adjust head positions with respect to the track of a disk.
On the shaft of the fine stepper motor, a second lead screw is provided. One end of a lever is moved by the second lead screw, and by the other end of the lever, the first lead screw is axially displaced against the force of a spring.
However, to smoothly transmit driving forces from the second lead screw to the one end of the lever, a certain backlash is needed between them, so that the fine displacement of the head becomes difficult due to play produced at the time when the fine stepper motor is changed from normal rotation to reverse rotation, or vice versa.
To avoid such a backlash, if the lever is partly made of elastic material, the elastic portion of the lever must hinder the accurate transmission of the driving forces, so that the fine displacement of the head becomes likewise difficult.
Furthermore, in the apparatus having such a second lead screw, the output of the fine stepper motor must become rather large, so that it is difficult to make the motor small in size and high in rotation.